Fibre optic gyroscopes for measuring rotation rates based on the Sagnac effect are known. When light traverses an optic fibre loop which is rotating about an axis perpendicular to its plane, the optical transmit time of the light varies in dependence on the loop's rotation rate. For two optical signals traversing the loop in opposite directions the Sagnac phase difference between them is proportional to the rotation rate.
Integrated optical circuits for use with such fibre optic gyroscopes have been proposed, for example, in U.S. Pat. No. 5,194,917. However, the design of these has been such as to include non-silicon passive functional elements. This adds extra complexity and expense to the manufacturing process due to extra alignment and fabrication stages required to try to avoid or minimise problems due to material mis-match and/or coupling losses.
The present invention seeks to avoid or reduce these difficulties experienced with the prior art.